The present invention relates to mixing arrangements for use in tanks, and more particularly to mixing arrangements which utilize radial flow impellers.
Radial flow impellers have long been used in continuous flow mixing systems. Such systems have, for example, been used for copper extraction applications and may accomplish their extraction operation by rotating a radial flow impeller near the base of a mixing chamber to expedite the flow of a mineral rich solution into the mixing chamber through a draft opening in the base of the chamber. Such applications are commonly referred to as pumper-mixers or lifter turbines. Exemplary systems using radial flow impellers include those described in U.S. Pat. Nos. 3,233,876, 4,207,275, 5,501,523 and 5,511,881. Other types of mixing systems, including batch systems, utilizing radial flow impellers are also known.
Many prior art radial flow impellers used in such systems consist of a flat plate cap and blades of uniform height positioned generally along the radial direction of the lower surface of the plate. Because the cap is flat and the blades are a uniform height, each blade extends a uniform depth below the cap all along its length from the inner to the outer radius of the cap. While in some applications the blades may trace the radii of the plate exactly, it is also known to use curved blades. Where the blades are of uniform height, and because adjacent blades necessarily are positioned closer to one another at the inner radius of the plate than at the outer radius of the plate, there is an increase in flow area between blades as fluid is pumped from the inner to the outer edge of the radial flow impeller. As a result of this increase in flow area, the flow velocity of fluids that are being pumped decreases near the outer radius of the impeller causing losses in pumping efficiency.
Accordingly, it would be desirable to provide mixing systems incorporating an improved radial flow impeller assembly.
In one aspect, a continuous flow mixing system for mixing two materials entering an inlet port of a tank, the tank including an outlet positioned above the inlet, is provided. The system includes a drive shaft extending within the tank and aligned with the inlet port. An impeller assembly including a plurality of blades and a cap member is coupled to the drive shaft to be rotated by the drive shaft. The plurality of blades extend radially outwardly, each blade including a lower side, the lower sides being substantially coplanar and lying adjacent the inlet port of the tank, each blade including an upper side. The cap member includes a substantially planar portion and a frusto-conical portion extending radially outward from the substantially planar portion and terminating in a circular rim. Rotation of the impeller assembly produces a head pressure for drawing material in the inlet port and raising a fluid level in the tank to at least a level of the tank outlet. The upper side of each blade is positioned adjacent an inner surface of the cap member and the lower side of each blade is positioned below a plane defied by the circular rim. A radially inner end of each blade is spaced between a central axis of the cap member and an intersection circle defined by intersection of the substantially planar portion and the frusto-conical portion. Each blade extends radially outwardly to at least the circular rim. A radius of the intersection circle is between about thirty percent (30%) and about sixty percent (60%) of a radius of the circular rim. A radial flow area defined by the inner surface of the cap member and adjacent blades of the impeller assembly remains substantially constant from a radial point starting at the intersection circle and extending to the circular rim.
In another aspect, a continuous flow mixing system for mixing two materials entering an inlet port of a tank, the tank including an outlet positioned above the inlet, is provided. The mixing system includes a drive shaft extending within the tank and aligned with the inlet port. An impeller assembly including a plurality of blades and a cap member is coupled to the drive shaft to be rotated by the drive shaft. The plurality of blades extends radially outwardly, each blade including a lower side, the lower sides being substantially coplanar and lying adjacent the inlet port of the tank, each blade including an upper side. The cap member includes a substantially planar portion and a frusto-conical portion extends radially outward from the substantially planar portion and terminates in a circular rim. Rotation of the impeller assembly produces a head pressure for drawing material in the inlet port and raising a fluid level in the tank to at least a level of the tank outlet. The upper side of each blade is positioned adjacent an inner surface of the cap member and the lower side of each blade is positioned below a plane defined by the circular rim. A radial flow area defined by the inner surface of the cap member and adjacent blades of the impeller assembly remains substantially constant from a radial point starting at an intersection circle and extending radially outward therefrom.
In a further aspect, a mixing system for a tank includes a drive shaft extending within the tank and a stationary tube centrally disposed and submerged within the tank, the tube having an upper opening and a lower opening. An impeller assembly including a plurality of blades and a cap member is coupled to the drive shaft to be rotated by the drive shaft. The plurality of blades extend radially outwardly, each blade including an exposed side, the exposed sides being substantially coplanar and lying adjacent the lower opening of the tube, each blade including a covered side. The cap member includes a substantially planar portion and a frusto-conical portion extending radially outward from the substantially planar portion, the frusto-conical portion terminating in a circular rim. Rotation of the impeller assembly draws material in the upper opening of the tube, down through in the tube, out the lower opening of the tube, and back upward along an annular spaced defined between the tube and the tank. The covered side of each blade is positioned adjacent an inner surface of the cap member and the exposed side of each blade is positioned above a plane defied by the circular rim. A radial flow area defined by the inner surface of the cap member and adjacent blades of the impeller assembly remains substantially constant from a radial point starting at an intersection circle defined by intersection of the substantially planar portion and the frusto-conical portion and extending radially outward from the intersection circle.
In another aspect, a mixing system for a tank includes a drive shaft and an impeller assembly. The drive shaft extends within the tank and the impeller assembly is coupled to the drive shaft to be rotated by the drive shaft. The impeller assembly includes a plurality of blades and a cap member. The blades extending radially outwardly, each blade including an exposed side, the exposed sides being substantially coplanar and lying adjacent flow opening of the tank, each blade including a covered side. The cap member includes a substantially planar portion and a frusto-conical portion extending radially outwardly from the substantially planar portion and terminating in a circular rim, rotation of the impeller assembly causing a flow out of the flow opening and through the impeller assembly. The covered side of each blade is positioned adjacent an inner surface of the cap member and the exposed side of each blade is spaced from a plane defined by the circular rim.
In yet another aspect, a mixing system includes an impeller assembly having a plurality of blades and a cap member. The blades extend radially outwardly, each blade including an exposed side, the exposed sides being substantially coplanar, each blade including a covered side. The cap member has an inner surface including a substantially planar portion and a frusto-conical portion extending radially outward from the substantially planar portion and terminating in a circular rim. The covered side of each blade is positioned adjacent the inner surface of the cap member and the exposed side of each blade is spaced away from a plane defied by the circular rim. A radially inner end of each blade is spaced between the central axis of the cap member and an intersection circle defined by intersection of the substantially planar portion and the frusto-conical portion. A radius of the intersection circle is between about thirty percent (30%) and about sixty percent (60%) of a radius of the circular rim. A radial flow area defined by the inner surface of the cap member and adjacent blades of the impeller assembly remains substantially constant from a radial point starting at the intersection circle and extending to the circular rim.
In yet a further aspect, a mixing system includes an impeller assembly having a plurality of blades and a cap member. The blades extend radially outwardly away from a central axis of the assembly, each blade including an exposed side, the exposed sides being substantially coplanar, each blade including a covered side. The cap member has an inner surface including a frusto-conical portion extending radially outward away from the central axis and terminating in a circular rim. The covered side of each blade is positioned adjacent the inner surface of the cap member and the exposed side of each blade is spaced away from a plane defined by the circular rim. A radially inner end of each blade is spaced from the central axis of the cap member and an outer tip of each blade extends at least to the circular rim. A covered blade height is between about sixty-six percent (66%) and about two-hundred thirty-three percent (233%) of an exposed blade height. A plurality of flow channels are defined by the frusto-conical inner surface portion of the cap member, adjacent blades of the impeller assembly and a plane defined by the exposed sides of the blades and the flow area of each flow channel remains substantially constant along its entire radial length.